WHOI Theseshttp://hdl.handle.net/1912/11722015-08-02T18:27:52Z2015-08-02T18:27:52ZPhysical control of the distributions of a key Arctic copepod in the northeast Chukchi SeaElliott, Stephen M.http://hdl.handle.net/1912/73662015-06-30T09:10:25Z2015-06-01T00:00:00ZPhysical control of the distributions of a key Arctic copepod in the northeast Chukchi Sea
Elliott, Stephen M.
The copepod Calanus glacialis is one of the most important zooplankton taxa in the Arctic shelf
seas where it serves as a key grazer, predator, and food source. Its summer distribution and
abundance have direct effects on much of the food web, from blooming phytoplankton to
migrating bowhead whales. The Chukchi Sea represents a highly advective regime dominated
by a barotropicly driven northward flow modulated by wind driven currents that reach the
bottom boundary layer of this shallow environment. In addition, a general northward gradient of
decreasing temperature and food concentration leads to geographically divergent copepod
growth and development rates. The physics of this system establish the connection potential
between specific regions. Unless biological factors are uniform and ideal the true connections
will be an uneven subset of this physically derived connection potential. In August 2012 and
2013, C. glacialis distributions were observed over Hanna Shoal in the northeast Chukchi Sea.
Here we used the Finite Volume Community Ocean Model i-State Configuration Model to
advect these distributions forward and back in time to determine the source and sink regions of
the transient Hanna Shoal C. glacialis population. We found that Hanna Shoal supplies diapause
competent C. glacialis to both the Beaufort Slope and the Chukchi Cap, mainly receives
juveniles from the broad slope between Hanna Shoal and Herald Canyon and receives second
year adults from as far as the Anadyr Gulf and as close as the broad slope between Hanna Shoal
and Herald Canyon. These connection potentials were not sensitive to precise times and
locations of release, but were quite sensitive to depth of release. Deeper particles often traveled
further than shallow particles due to strong vertical shear in the shallow Chukchi. The 2013 sink
region was shifted west relative to the 2012 region and the 2013 adult source region was shifted
north relative to the 2012 region.
Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2015
2015-06-01T00:00:00ZStrong wind events across Greenland’s coast and their influence on the ice sheet, sea ice and oceanOltmanns, Marilenahttp://hdl.handle.net/1912/73532015-06-19T09:09:11Z2015-06-01T00:00:00ZStrong wind events across Greenland’s coast and their influence on the ice sheet, sea ice and ocean
Oltmanns, Marilena
In winter, Greenland’s coastline adjacent to the subpolar North Atlantic and
Nordic Seas is characterized by a large land-sea temperature contrast. Therefore,
winds across the coast advect air across a horizontal temperature gradient and can
result in significant surface heat fluxes both over the ice sheet (during onshore winds)
and over the ocean (during offshore winds). Despite their importance, these winds
have not been investigated in detail, and this thesis includes the first comprehensive
study of their characteristics, dynamics and impacts. Using an atmospheric reanalysis,
observations from local weather stations, and remote sensing data, it is suggested
that high-speed wind events across the coast are triggered by the superposition of
an upper level potential vorticity anomaly on a stationary topographic Rossby wave
over Greenland, and that they intensify through baroclinic instability. Onshore winds
across Greenland’s coast can result in increased melting, and offshore winds drive large
heat losses over major ocean convection sites.
Strong offshore winds across the southeast coast are unique over Greenland, because
the flow is funneled from the vast ice sheet inland into the narrow valley of
Ammassalik at the coast, where it can reach hurricane intensity. In this region, the
cold air, which formed over the northern ice sheet, is suddenly released during intense
downslope wind events and spills over the Irminger Sea where the cold and strong
winds can drive heat fluxes of up to 1000 W m−2, with potential implications for deep
water formation. Moreover, the winds advect sea ice away from the coast and out of
a major glacial fjord.
Simulations of these wind events in Ammassalik with the atmospheric Weather
Research and Forecast Model show that mountain wave dynamics contribute to the
acceleration of the downslope flow. In order to capture these dynamics, a high model resolution with a detailed topography is needed. The effects of using a different
resolution locally in the valley extend far downstream over the Irminger Sea, which
has implications for the evolution and distribution of the heat fluxes.
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2015
2015-06-01T00:00:00ZA magmatic trigger for the Paleocene-Eocene Thermal Maximum?Dubin, Andrea R.http://hdl.handle.net/1912/73522015-06-19T09:09:07Z2015-06-01T00:00:00ZA magmatic trigger for the Paleocene-Eocene Thermal Maximum?
Dubin, Andrea R.
Fifty-six million years ago Earth experienced rapid global warming (~6°C) that was
caused by the release of large amounts of carbon into the ocean-atmosphere system. This
Paleocene-Eocene Thermal Maximum (PETM) is often cited as an analogue of anthropogenic
climate change. Many trigger mechanisms for the carbon release at the PETM have been
proposed. Common to all scenarios is rapid release of isotopically light carbon (<13C/12C values)
from methane hydrates, terrestrial or marine organic matter, as indicated by a pronounced
excursion to light carbon isotope values across the PETM. I test the hypothesis that the PETM
warming and isotope excursion were caused by the intrusion of a magmatic sill complex into
organic-rich sediments in the North Atlantic. The intrusion of magma into sedimentary rocks
will cause heating and metamorphic reactions in a thermal aureole around the intrusion. If these
sediments are rich in organic matter, large volumes of isotopically light carbon are rapidly
released. I examine geochemical evidence from lead, osmium, and organic carbon to place
constraints on the extent the carbon isotope excursion during the PETM may have been caused
by contact metamorphism of organic-rich sediments. Potential terrestrial and submarine analogs
are examined to determine the behavior of these elements during thermal alteration. Furthermore,
geochemical evidence from sediment cores at the PETM provides additional information about
what might have caused the carbon isotope excursion. I find that lead is not a suitable proxy for
carbon mobilization to the overlying seawater during contact metamorphism. Osmium, however,
is mobilized together with carbon. Making reasonable assumptions for the 187Os/188Os of the
sediments from the North Atlantic Magmatic Province (NAMP), constrained by the 187Re/188Os
of organic-rich sediments and the depositional age of the sediment, the entire marine osmium
isotope anomaly at the PETM could be explained without the need to invoke enhanced
continental weathering. Based on estimates of the extent of mobilization of organic carbon
relative to osmium, approximately 47% to 60% of the carbon released at the PETM may have
been derived from thermal alteration of organic-rich sediments in the NAMP.
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2015
2015-06-01T00:00:00ZUsing passive samplers to assess bioavailability, toxicity, and reactivity of hydrophobic organic chemicals (HOCs)Tcaciuc, Alexandra P.http://hdl.handle.net/1912/73052015-05-23T09:08:55Z2015-06-01T00:00:00ZUsing passive samplers to assess bioavailability, toxicity, and reactivity of hydrophobic organic chemicals (HOCs)
Tcaciuc, Alexandra P.
Hydrophobic organic chemicals (HOCs) are a class of environmental contaminants responsible
for numerous acute and chronic health effects in humans and wildlife. This thesis illustrates three
applications of polyethylene (PE) passive sampling, which enhance our toolbox for estimating
environmental hazards associated with HOCs.
First, we present a methodology that can be used to estimate the bioaccumulation potential of
numerous organic chemicals based on passive sampling and comprehensive two dimensional gas
chromatography (GC × GC). Using GC × GC retention times, we show that lipid-water and samplerwater
partition coefficients can be estimated within a factor of 2 and 3, respectively. The method
was then applied to estimate body burdens of various HOCs in benthic organisms from GC × GC
analysis of PE equilibrated with contaminated sediment. Empirical observations of accumulation in
the Nereis virens polychaete were in good agreement with PE-based predictions for PCBs, but were
lower by at least an order of magnitude for other classes of HOCs (such as PAHs) presumably due to
metabolism.
Second, we applied the same methodology to a set of contaminated sediments and estimated
the cumulative baseline toxicity associated with environmental mixtures of HOCs. The predictions
were compared against empirical measurements of baseline toxicity using the water flea Daphnia
magna. The estimated total body burdens of HOCs were in good agreement with measured toxicity,
with toxicity occurring at body burdens larger than 30 mg/glipid. In contrast, the toxicity estimated
based on priority pollutants severely underestimated the observed toxicity, emphasizing the
importance of cumulative effects.
Lastly, to advance our understanding of the processes that affect passive sampling results in situ
(when they are operating away from equilibrium), a mathematical model was developed for
reactive chemicals transferring between PE and sediment beds. The reaction diffusion model was
used to infer in situ degradation rates of dichlorodiphenyltrichloroethane (DDT), which in the
sediments of a freshwater lake were found to be between 0.09 and 0.9 d-1. A second mathematical
model describing the kinetics of exchange between passive samplers and water was also developed,
which can be used in both field (infinite baths) and laboratory (finite baths) conditions.
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute Of Technology and the Woods Hole Oceanographic Institution June 2015
2015-06-01T00:00:00Z